Implement Two-Pointer AlgorithmsStep 3 of 5

Reverse a List In Place

12345

Step 3: Reverse a List In Place

Implement reverse_in_place(arr) which reverses the list in place using two pointers and returns the same list object.

Swap the elements at the left and right pointers, then move the pointers toward each other. Do not allocate a new list. Lists with zero or one element are already reversed.

Hints
Starter code
def two_sum_sorted(nums, target):
    i, j = 0, len(nums) - 1
    while i < j:
        s = nums[i] + nums[j]
        if s == target:
            return (i, j)
        elif s < target:
            i += 1
        else:
            j -= 1
    return None


def is_palindrome(s):
    i, j = 0, len(s) - 1
    while i < j:
        while i < j and not s[i].isalnum():
            i += 1
        while i < j and not s[j].isalnum():
            j -= 1
        if s[i].lower() != s[j].lower():
            return False
        i += 1
        j -= 1
    return True


def reverse_in_place(arr):
    """Reverse arr in place with two pointers and return it."""
    # TODO: swap arr[i] and arr[j] while moving the pointers inward
    pass
Write it on a laptop

The editor and the test runner need a wide screen. Open this page on a desktop browser and your progress will be waiting.

PreviousNext step